Composite paper sheets produced by mixing carbon fibers with polyvinyl alcohol fibers or pulp and shaping the resultant mixture in the form of sheet are known as carbon fiber paper and have been used as electroconductive elements, for example. Such carbon fiber sheet, however, has a relatively high electric resistance and is deficient in mechanical strength. Further, the pulp or polyvinyl alcohol fibers have low resistance to heat and corrosion. Thus, the carbon fiber paper sheet fails to function satisfactorily when it is used as a base sheet for electrodes in fuel batteries, for example. In order to impart desirable properties such as high electroconductivity and mechanical strength to carbon fiber paper, attempts have been made to join and immobilize points of mutual contact of the individual carbon fibers in the paper by impregnating the mixed paper sheet prepared as described above with a solution having a phenol resin dissolved in such solvent as methanol. The impregnated mixed paper sheet is then heated to a temperature of not less than 800.degree. C within an atmosphere of an inert gas. In all of these methods, the carbon fiber paper thus produced still to acquire properties suitable for use as an electroconductive element.
Thus, there exists a need for provision of a carbon fiber paper which has high electroconductivity, mechanical strength and resistance to corrosion.